U.S. patent number 11,126,081 [Application Number 16/473,992] was granted by the patent office on 2021-09-21 for photopolymer composition.
This patent grant is currently assigned to LG CHEM, LTD.. The grantee listed for this patent is LG CHEM, LTD.. Invention is credited to Yeong Rae Chang, Seok Hoon Jang, Boo Kyung Kim, Heon Kim.
United States Patent |
11,126,081 |
Kim , et al. |
September 21, 2021 |
Photopolymer composition
Abstract
The present disclosure relates to a photopolymer composition
including: a polymer matrix or a precursor thereof; a photoreactive
monomer including a polyfunctional (meth)acrylate monomer having a
refractive index of 1.5 or less and a viscosity at 25.degree. C. of
100 cps or less, and a monofunctional (meth)acrylate monomer having
a refractive index of 1.5 or more; and a photoinitiator, wherein a
content of the monofunctional (meth)acrylate monomer having a
refractive index of 1.5 or more in the photoreactive monomer is 60
wt % or more. The present disclosure also relates to a hologram
recording medium produced from the photopolymer composition, an
optical element including the hologram recording medium, and a
holographic recording method using the photopolymer
composition.
Inventors: |
Kim; Boo Kyung (Daejeon,
KR), Kim; Heon (Daejeon, KR), Jang; Seok
Hoon (Daejeon, KR), Chang; Yeong Rae (Daejeon,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
N/A |
KR |
|
|
Assignee: |
LG CHEM, LTD. (Seoul,
KR)
|
Family
ID: |
63918417 |
Appl.
No.: |
16/473,992 |
Filed: |
March 14, 2018 |
PCT
Filed: |
March 14, 2018 |
PCT No.: |
PCT/KR2018/003002 |
371(c)(1),(2),(4) Date: |
June 26, 2019 |
PCT
Pub. No.: |
WO2018/199467 |
PCT
Pub. Date: |
January 11, 2018 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20190339612 A1 |
Nov 7, 2019 |
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Foreign Application Priority Data
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Apr 25, 2017 [KR] |
|
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10-2017-0053106 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F
7/027 (20130101); C08F 220/1804 (20200201); G03F
7/035 (20130101); G03H 1/02 (20130101); C08G
18/72 (20130101); G03F 7/001 (20130101); C08L
75/14 (20130101); C08F 2/50 (20130101); C08G
18/40 (20130101); C09D 4/00 (20130101); G11B
7/24044 (20130101); C08G 18/6229 (20130101); C08F
299/0435 (20130101); G11B 7/245 (20130101); C09D
4/06 (20130101); C09D 175/16 (20130101); C08F
283/006 (20130101); C08F 220/26 (20130101); C09D
175/14 (20130101); C09D 4/06 (20130101); C08F
283/006 (20130101); C09D 4/00 (20130101); C08F
220/286 (20200201); C08F 283/006 (20130101); C08F
220/18 (20130101); C08F 222/1006 (20130101); G03H
2260/12 (20130101); C08F 222/103 (20200201); C08F
222/102 (20200201); C08F 220/1804 (20200201); C08F
220/14 (20130101); C08F 220/20 (20130101) |
Current International
Class: |
G03H
1/02 (20060101); G03F 7/00 (20060101); C08G
18/62 (20060101); C08G 18/40 (20060101); C08F
299/04 (20060101); C08F 220/18 (20060101); G03F
7/004 (20060101); C08G 18/72 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2000-344716 |
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Dec 2000 |
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JP |
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2002-293762 |
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Oct 2002 |
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JP |
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2005-181955 |
|
Jul 2005 |
|
JP |
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2005189720 |
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Jul 2005 |
|
JP |
|
2012082386 |
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Apr 2012 |
|
JP |
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2013510204 |
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Mar 2013 |
|
JP |
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2013231153 |
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Nov 2013 |
|
JP |
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2014063104 |
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Apr 2014 |
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JP |
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1020050069135 |
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Jul 2005 |
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KR |
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1020060078556 |
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Jul 2006 |
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KR |
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1020100022910 |
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10-2011-0115324 |
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KR |
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1020120101431 |
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KR |
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1020130006421 |
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Jan 2013 |
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KR |
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102010049584 |
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Apr 2014 |
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KR |
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1020150120627 |
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Oct 2015 |
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KR |
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1020170015904 |
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Feb 2017 |
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KR |
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02/39185 |
|
May 2002 |
|
WO |
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2008015983 |
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Feb 2008 |
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WO |
|
Other References
Machine translation of JP 2005-181955 (2005). cited by examiner
.
Machine translation of JP 2013-231153 (2013). cited by examiner
.
Machine translation of JP 2002-293762 (2002). cited by examiner
.
Machine transaltino of JP 2000-344716 (2000). cited by
examiner.
|
Primary Examiner: Angebranndt; Martin J
Attorney, Agent or Firm: Dentons US LLP
Claims
The invention claimed is:
1. A photopolymer composition, comprising: a polymer matrix or a
precursor thereof; a photoreactive monomer mixture comprising a
polyfunctional (meth)acrylate monomer having a refractive index of
1.5 or less and a viscosity at 25.degree. C. of 100 cps or less,
and a monofunctional (meth)acrylate monomer having a refractive
index of 1.5 or more; and a photoinitiator, wherein the content of
the monofunctional (meth)acrylate monomer in the photoreactive
monomer mixture is 70 wt % to 90 wt %, wherein the polymer matrix
is a reaction product of a compound having at least one isocyanate
group and a polyol, and wherein the polyol has a hydroxyl
equivalent weight of 300 g/mol to 10,000 g/mol, and a weight
average molecular weight of 100,000 to 1,500,000 g/mol.
2. The photopolymer composition of claim 1, wherein the
monofunctional (meth)acrylate monomer has a viscosity at 25.degree.
C. of 300 cps or less.
3. The photopolymer composition of claim 1, wherein the
polyfunctional (meth)acrylate monomer comprises an ether bond, and
the monofunctional (meth)acrylate monomer comprises an ether bond
and a fluorene functional group.
4. The photopolymer composition of claim 1, wherein each of the
polyfunctional (meth)acrylate monomer and the monofunctional
(meth)acrylate monomer has a weight average molecular weight of 50
to 1000 g/mol.
5. The photopolymer composition of claim 1, wherein a refractive
index of the polymer matrix or the precursor thereof is higher than
the refractive index of the polyfunctional (meth)acrylate monomer
and lower than the refractive index of the monofunctional
(meth)acrylate monomer.
6. The photopolymer composition of claim 1, comprising: 20 wt % to
80 wt % of the polymer matrix or the precursor thereof; 10 wt % to
70 wt % of the photoreactive monomer mixture; and 0.1 wt % to 15 wt
% of the photoinitiator.
7. A hologram recording medium produced from the photopolymer
composition of claim 1.
8. An optical element comprising the hologram recording medium of
claim 7.
9. A holographic recording method comprising selectively
polymerizing the photoreactive monomer mixture contained in the
photopolymer composition of claim 1 using electromagnetic
radiation.
10. The photopolymer composition of claim 1, further comprising a
catalyst.
11. The photopolymer composition of claim 10, wherein the catalyst
is one or more selected from tin octanoate, zinc octanoate,
dibutyltin dilaurate, dimethylbis[(1-oxoneodecyl)oxy]stannane,
dimethyltin dicarboxylate, zirconium bis(ethylhexanoate), zirconium
acetylacetonate, 1,4-diazabicyclo[2.2.2]octane, diazabicyclononane,
diazabicyclo undecane, 1,1,3,3-tetramethylguanidine and
1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido(1,2-a)pyrimidine.
12. The polymer composition of claim 1, wherein the photoinitiator
is a monomolecular (type I) initiator or a bimolecular (type II)
initiator.
13. The polymer composition of claim 12, wherein the monomolecular
(type I) initiator is an aromatic ketone compounds in combination
with a tertiary amine.
14. The polymer composition of claim 13, wherein the aromatic
ketone compound is one or more selected from benzophenone,
alkylbenzophenone, 4,4'-bis(dimethylamino)benzophenone (Michler's
ketone), anthrone and halogenated benzophenone, and a mixture
thereof.
15. The polymer composition of claim 12, wherein the bimolecular
(type II) initiator is one or more selected from benzoin and
derivatives thereof, benzyl ketal,
2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylophosphine
oxide, phenylglyoxyl ester, camphorquinone,
.alpha.-aminoalkylphenone, .alpha...alpha.-dialkylacetophenone,
1-[4-(phenylthio)phenyl]octane-1,2-dione 2-(O-benzoyloxime), and
.alpha.-hydroxyalkylphenone.
16. The polymer composition of claim 1, wherein the photoinitiator
is a mixture of ammonium aryl borate and one or more dyes.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is a national stage of International Application
No. PCT/KR2018/003002 filed Mar. 14, 2018, which claims the
benefits of Korean Patent Application No. 10-2017-0053106 filed on
Apr. 25, 2017, with the Korean Intellectual Property Office, the
disclosures of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
The present disclosure relates to a photopolymer composition, a
hologram recording medium, an optical element, and a holographic
recording method.
BACKGROUND OF ART
A hologram recording medium records information by changing a
refractive index in a holographic recording layer in the medium
through an exposure process, reads the variation of refractive
index in the medium thus recorded, and reproduces the
information.
When a photopolymer (photosensitive resin) is used, the light
interference pattern can be easily stored as a hologram by
photopolymerization of the low molecular weight monomer. Therefore,
the photopolymer can be used in various fields such as for optical
lenses, mirrors, deflecting mirrors, filters, diffusing screens,
diffraction elements, light guides, waveguides, holographic optical
elements having projection screen and/or mask functions, media of
optical memory systems and light diffusion plates, optical
wavelength multiplexers, reflection type and transmission type
color filters, and the like.
Typically, a photopolymer composition for hologram production
includes a polymer binder, a monomer, and a photoinitiator, and a
photosensitive film produced from such a composition is irradiated
with laser interference light to induce photopolymerization of
local monomers.
In a portion where a relatively large number of monomers are
present in such photopolymerization process, the refractive index
becomes high. Further, in a portion where a relatively large number
of polymer binders are present, the refractive index is relatively
lowered and thus refractive index modulation occurs, and a
diffraction grating is generated by such refractive index
modulation. The refractive index modulation value (.DELTA.n) is
influenced by the thickness and the diffraction efficiency (DE) of
the photopolymer layer, and the angular selectivity increases as
the thickness decreases.
Recently, development of materials capable of maintaining a stable
hologram with high diffraction efficiency has been demanded, and
also various attempts have been made to manufacture a photopolymer
layer having a thin thickness and a high refractive index
modulation value.
DETAILED DESCRIPTION OF THE INVENTION
Technical Problem
The present disclosure is to provide a photopolymer composition
which can more easily provide a photopolymer layer having a high
refractive index modulation value even with a thin thickness.
The present disclosure is also to provide a hologram recording
medium including a photopolymer layer having a high refractive
index modulation value even with a thin thickness.
The present disclosure is also to provide an optical element
including the above-described hologram recording medium.
The present disclosure is also to provide a holographic recording
method including selectively polymerizing photoreactive monomers
contained in the photopolymer composition using electromagnetic
radiation.
Technical Solution
The present disclosure provides a photopolymer composition
including: a polymer matrix or a precursor thereof; a photoreactive
monomer including a polyfunctional (meth)acrylate monomer having a
refractive index of 1.5 or less and a viscosity at 25.degree. C. of
100 cps or less, and a monofunctional (meth)acrylate monomer having
a refractive index of 1.5 or more; and a photoinitiator, wherein a
content of the monofunctional (meth)acrylate monomer having a
refractive index of 1.5 or more in the photoreactive monomer is 60
wt % or more.
The present disclosure also provides a hologram recording medium
produced from the photopolymer composition.
In addition, the present disclosure provides an optical element
including the hologram recording medium.
The present disclosure also provides a holographic recording method
including selectively polymerizing photoreactive monomers contained
in the photopolymer composition using electromagnetic
radiation.
Hereinafter, the photopolymer composition, the hologram recording
medium, the optical element, and the holographic recording method
according to a specific embodiment of the present invention will be
described in more detail.
As used herein, the term "(meth)acrylate" refers to either
methacrylate or acrylate.
Further, the term "hologram" as used herein refers to a recording
medium in which optical information is recorded in an entire
visible range and a near ultraviolet range (300 to 800 nm) through
an exposure process, and examples thereof include all of visual
holograms such as in-line (Gabor) holograms, off-axis holograms,
full-aperture transfer holograms, white light transmission
holograms ("rainbow holograms"), Denisyuk holograms, off-axis
reflection holograms, edge-lit holograms, and holographic
stereograms.
According to an embodiment of the present disclosure, a
photopolymer composition is provided, including: a polymer matrix
or a precursor thereof; a photoreactive monomer including a
polyfunctional (meth)acrylate monomer having a refractive index of
1.5 or less and a viscosity at 25.degree. C. of 100 cps or less,
and a monofunctional (meth)acrylate monomer having a refractive
index of 1.5 or more; and a photoinitiator, wherein a content of
the monofunctional (meth)acrylate monomer having a refractive index
of 1.5 or more in the photoreactive monomer is 60 wt % or more.
The present inventors found through experiments that holograms
produced by using a polyfunctional recording monomer having a
relatively low refractive index and a low viscosity at room
temperature and a monofunctional recording monomer having a
relatively high refractive index with the monofunctional monomer in
a predetermined amount or more can exhibit a significantly improved
refractive index modulation value as compared with the existing
holograms even with a thin thickness, thereby completing the
present invention.
More specifically, the photopolymer composition includes a
photoreactive monomer including a polyfunctional (meth)acrylate
monomer having a refractive index of 1.5 or less and a viscosity at
25.degree. C. of 100 cps or less, or 90 cps or less, and a
monofunctional (meth)acrylate monomer having a refractive index of
1.5 or more, and a content of the monofunctional (meth)acrylate
monomer having a refractive index of 1.5 or more in the
photoreactive monomer is 60 wt % or more, or 65 wt % or more.
Accordingly, the hologram produced from the photopolymer
composition can exhibit a refractive index modulation value
(.DELTA.n) of 0.01 or more, or 0.0120 or more, even at a thickness
of 5 .mu.m to 30 .mu.m.
In particular, the photopolymer composition includes a
polyfunctional (meth)acrylate monomer having a viscosity 25.degree.
C. of 100 cps or less, or 90 cps or less, and this polyfunctional
acrylate can increase the cross-linking point to compensate for the
low cross-linking density of the monofunctional (meth)acrylate
which is used for improving the refractive index.
The photopolymer composition includes 60 wt % or more, 65 wt % or
more, or 70 wt % to 90 wt % of the monofunctional (meth)acrylate
monomer having a relatively high refractive index in the
photoreactive monomer, thereby increasing a difference in the
refractive index with respect to the binder. Accordingly, as
described above, the hologram produced from the photopolymer
composition can achieve a refractive index modulation value
(.DELTA.n) of 0.0100 or more, or 0.0120 or more, even at a
thickness of 5 .mu.m to 30 .mu.m.
Meanwhile, the monofunctional (meth)acrylate monomer having a
refractive index of 1.5 or more may have a relatively high
viscosity as compared with the polyfunctional (meth)acrylate
monomer. Specifically, the monofunctional (meth)acrylate monomer
having a refractive index of 1.5 or more may have a viscosity at
25.degree. C. of 300 cps or less, or 100 cps to 300 cps.
As the photoreactive monomer, a (meth)acrylate-based
.alpha.,.beta.-unsaturated carboxylic acid derivative such as
(meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, or
(meth)acrylic acid may be used.
More specifically, the polyfunctional (meth)acrylate monomer having
a refractive index of 1.5 or less and a viscosity at 25.degree. C.
of 100 cps or less, or 90 cps or less, may include an ether bond
and a fluorene functional group in the molecule. Specific examples
of the polyfunctional (meth)acrylate monomer having a refractive
index of 1.5 or less and a viscosity at 25.degree. C. of 100 cps or
less, or 90 cps or less, include polyethylene glycol
di(meth)acrylate, trimethylpropane (ethylene oxide)
tri(meth)acrylate, and the like.
In addition, the monofunctional (meth)acrylate monomer having a
refractive index of 1.5 or more may include an ether bond and a
fluorene functional group in the molecule. Specific examples of the
monofunctional (meth)acrylate monomer having a refractive index of
1.5 or more include phenoxybenzyl (meth)acrylate, o-phenylphenol
ethylene oxide (meth)acrylate, benzyl (meth)acrylate,
2-(phenylthio)ethyl (meth)acrylate, biphenylmethyl (meth)acrylate,
and the like.
Each of the polyfunctional (meth)acrylate monomer having a
refractive index of 1.5 or less and a viscosity at 25.degree. C. of
100 cps or less, or 90 cps or less, and the monofunctional
(meth)acrylate monomer having a refractive index of 1.5 or more,
may have a weight average molecular weight of 50 to 1000 g/mol, or
200 to 600 g/mol. The weight average molecular weight refers to a
weight average molecular weight using polystyrene calibration
measured by a GPC method.
The glass transition temperature of the polyfunctional
(meth)acrylate monomer and the monofunctional (meth)acrylate
monomer can be measured by differential scanning calorimetry or by
a commonly known method.
The polymer matrix may serve as a support for the photopolymer
composition and a final product produced therefrom such as a film,
and may increase the refractive index modulation of the hologram
produced from the photopolymer composition due to a difference in
the refractive index.
The polymer matrix may be a reaction product of a compound having
at least one isocyanate group and a polyol.
The compound having at least one isocyanate group may be a known
compound having an average of at least one NCO functional group per
molecule, or a mixture thereof, and may be a compound having at
least one isocyanate group.
More specifically, the compound having at least one isocyanate
group is an aliphatic, cycloaliphatic, aromatic, or
aromatic-aliphatic mono-, di-, tri-, or poly-isocyanate. The
compound having at least one isocyanate group may be secondary
products with relatively high molecular weight (oligo- and
poly-isocyanates) of monomer-type di- and/or tri-isocyanates having
urethane, urea, carbodiimide, acylurea, isocyanurate, allophanate,
biuret, oxadiazinetrione, uretdione, or iminooxadiazinedione
structures.
Specific examples of the compound having at least one isocyanate
group include butylene diisocyanate, hexamethylene diisocyanate
(HDI), isophorone diisocyanate (IPDI),
1,8-diisocyanato-4-(isocyanatomethyl)octane, 2,2,4- and/or
2,4,4-trimethylhexamethylene diisocyanate, isomeric
bis(4,4'-isocyanato-cyclohexyl)methane, a mixture thereof with any
desired isomer content, isocyanatomethyl-1,8-octane diisocyanate,
1,4-cyclohexylene diisocyanate, isomeric cyclohexane dimethylene
diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene
diisocyanate, 1,5-naphthylene diisocyanate, 2,4'- or
4,4'-diphenylmethane diisocyanate, and/or triphenylmethane
4,4',4''-triisocyanate, or the like.
The polyol which reacts with the compound having at least one
isocyanate group to form the polymer matrix may be an aliphatic,
aromatic-aliphatic, or cycloaliphatic diol, triol, and/or higher
polyol having 2 to 20 carbon atoms.
The polyol may have a hydroxyl equivalent weight of 300 g/mol to
10,000 g/mol, and a weight average molecular weight of 100,000 to
1,500,0000 g/mol.
Examples of the diols include ethylene glycol, diethylene glycol,
triethylene glycol, tetraethylene glycol, dipropylene glycol,
tripropylene glycol, 1,2-propanediol, 1,3-propanediol,
1,4-butanediol, neopentyl glycol, 2-ethyl-2-butylpropanediol,
trimethylpentanediol, positional isomers of diethyloctanediols,
1,3-butylene glycol, cyclohexanediol, 1,4-cyclohexane-dimethanol,
1,6-hexanediol, 1,2- and 1,4-cyclohexanediol, hydrogenated
bisphenol A (2,2-bis(4-hydroxycyclohexyl)propane) and
2,2-dimethyl-3-hydroxypropyl, and
2,2-dimethyl-3-hydroxypropionate.
Further, examples of the triols include trimethylolethane,
trimethylolpropane, and glycerol. Suitable high-functional alcohols
include ditrimethylolpropane, pentaerythritol, dipentaerythritol,
and sorbitol.
As the polyols, aliphatic and cycloaliphatic polyols having a
relatively large molecular weight, such as polyester polyols,
polyether polyols, polycarbonate polyols, hydroxy-functional
acrylic resins, hydroxy-functional polyurethanes,
hydroxy-functional epoxy resins, and the like may be used.
The polyester polyols may be linear polyester diols, as obtained in
a known manner from aliphatic, cycloaliphatic, or aromatic di- or
polycarboxylic acid or their anhydrides, for example, succinic
acid, glutaric acid, adipic acid, pimelic acid, suberic acid,
azelaic acid, sebacic acid, nonanedicarboxylic acid,
decanedicarboxylic acid, terephthalic acid, isophthalic acid,
o-phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid or
trimellitic acid, and acid anhydrides such as o-phthalic anhydride,
trimellitic anhydride, or succinic anhydride, or any mixtures
thereof, by using polyhydric alcohols such as ethanediol, di-,
tri-, or tetraethylene glycol, 1,2-propanediol, di-, tri-, or
tetrapropylene glycol, 1,3-propanediol, 1,4-butanediol,
1,3-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,
2,2-dimethyl-1,3-propanediol, 1,4-dihydroxycyclohexane,
1,4-dimethylolcyclohexane, 1,8-octanediol, 1,10-decanediol,
1,12-dodecanediol, or a mixture thereof, and optionally,
simultaneously using higher functional polyols such as trimethylol
propane or glycerol. Of course, cyclic aliphatic and/or aromatic
di- and polyhydroxy compounds are suitable as polyhydric alcohols
for the preparation of polyester polyols. It is also possible to
use the corresponding polycarboxylic acid anhydrides of the lower
alcohols or the corresponding polycarboxylates, or mixtures
thereof, instead of free polycarboxylic acids in the preparation of
the polyesters.
Further, the polyester polyols that can be used in the synthesis of
the polymer matrix include homo- or copolymers of lactones, which
are preferably obtained by an addition of lactones or lactone
mixtures, such as butyrolactone, .epsilon.-caprolactone, and/or
methyl-.epsilon.-caprolactone to suitable bifunctional and/or
higher functional initiator molecules, such as the aforementioned
polyhydric alcohols having a small molecular weight as the
synthetic component for the polyester polyols.
Further, the polycarbonates having hydroxyl groups are also
suitable as a polyhydroxy component for prepolymer synthesis. For
example, it may be prepared by reaction of diols such as
1,4-butanediol and/or 1,6-hexanediol and/or 3-methylpentanediol
with diaryl carbonates such as diphenyl carbonate, dimethyl
carbonate, or phosgene.
Further, the polyether polyol that can be used for the synthesis of
the polymer matrix may be, for example, polyaddition products of
styrene oxides, of ethylene oxide, of propylene oxide, of
tetrahydrofuran, of butylene oxide, or of epichlorohydrin, mixed
addition products thereof, grafting products thereof, polyether
polyols obtained by condensation of polyhydric alcohols or mixtures
thereof, and those obtained by alkoxylation of polyhydric alcohols,
amines and amino alcohols. Specific examples of the polyether
polyol include poly(propylene oxide)s, poly(ethylene oxide)s, and
combinations thereof in the form of random or block copolymers, or
poly(tetrahydrofuran)s and mixtures thereof having OH functionality
of 1.5 to 6 and a number average molecular weight of 200 to 18,000
g/mol, and preferably an OH functionality of 1.8 to 4.0 and a
number average molecular weight of 600 to 8000 g/mol, particularly
preferably an OH functionality of 1.9 to 3.1 and a number average
molecular weight of 650 to 4500 g/mol.
Meanwhile, the photopolymer composition of the embodiment includes
a photoinitiator. The photoinitiator is a compound which is
activated by light or actinic radiation, and initiates
polymerization of a compound containing a photoreactive functional
group such as the photoreactive monomer.
As the photoinitiator, commonly known photoinitiators can be used
without particular limitation. For example, a monomolecular (type
I) initiator or a bimolecular (type II) initiator may be used.
The (type I) system for free radical photopolymerization may
include, for example, an aromatic ketone compounds in combination
with a tertiary amine, such as benzophenone, alkylbenzophenone,
4,4'-bis(dimethylamino)benzophenone (Michler's ketone), anthrone
and halogenated benzophenone, or a mixture of these types.
Initiators (type II) such as benzoin and derivatives thereof,
benzyl ketal, acylphosphine oxide, for example,
2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylophosphine
oxide, phenylglyoxyl ester, camphorquinone,
alpha-aminoalkylphenone, alpha,alpha-dialkoxyacetophenone,
1-[4-(phenylthio)phenyl]octane-1,2-dione 2-(O-benzoyloxime), and
alpha-hydroxyalkylphenone are also suitable. A photoinitiator
system composed of a mixture of ammonium aryl borate and one or
more dyes may also be used as the photoinitiator.
The photopolymer composition may include: 20 wt % to 80 wt % of the
polymer matrix or the precursor thereof; 10 wt % to 70 wt % of the
photoreactive monomer; and 0.1 wt % to 15 wt % of the
photoinitiator, or may include: 30 wt % to 70 wt % of the polymer
matrix or the precursor thereof; 20 wt % to 60 wt % of the
photoreactive monomer; and 0.1 wt % to 10 wt % of the
photoinitiator.
The photopolymer composition may further include other additives,
catalysts, and the like. For example, the photopolymer composition
may further include a catalyst which is commonly known for
promoting polymerization of the polymer matrix or the photoreactive
monomer. Examples of the catalyst include tin octanoate, zinc
octanoate, dibutyltin dilaurate,
dimethylbis[(1-oxoneodecyl)oxy]stannane, dimethyltin dicarboxylate,
zirconium bis(ethylhexanoate), zirconium acetylacetonate, or
tertiary amines such as 1,4-diazabicyclo[2.2.2]octane,
diazabicyclononane, diazabicyclo undecane,
1,1,3,3-tetramethylguanidine,
1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido(1,2-a)pyrimidine, and
the like.
Meanwhile, according to another embodiment of the present
disclosure, a hologram recording medium produced from the
photopolymer composition may be provided.
As described above, when the photopolymer composition of one
embodiment is used, it is possible to provide holograms capable of
achieving a significantly improved refractive index modulation
value while having a thinner thickness, as compared with holograms
previously known in the art.
In the photopolymer composition of the one embodiment, the
respective components contained therein are homogeneously mixed,
dried, and cured at a temperature of 20.degree. C. or higher, and
then predetermined exposure procedures are undertaken, thereby
producing a hologram for optical application in the entire visible
range and the near ultraviolet region (300 to 800 nm).
In the photopolymer composition of the one embodiment, the other
components excluding the compound having at least one isocyanate
group for forming the polymer matrix or the precursor thereof may
be first homogeneously mixed, and then the compound having at least
one isocyanate group may be mixed with the catalyst to prepare
holograms.
In the photopolymer composition of one embodiment, a mixing device,
a stirrer, a mixer, or the like which are commonly used in the art
can be used for mixing the respective components contained therein
without particular limitation. The temperature in the mixing
process may be 0.degree. C. to 100.degree. C., preferably
10.degree. C. to 80.degree. C., and particularly preferably
20.degree. C. to 60.degree. C.
Meanwhile, the other components excluding the compound having at
least one isocyanate group for forming the polymer matrix or the
precursor thereof in the photopolymer composition of one embodiment
may be first homogeneously mixed. Subsequently, at the time of
adding the compound having at least one isocyanate group, the
photopolymer composition may become a liquid formulation that is
cured at a temperature of 20.degree. C. or more.
The curing temperature may vary depending on the composition of the
photopolymer and the curing is promoted, for example, by heating at
a temperature of from 30.degree. C. to 180.degree. C., preferably
40.degree. C. to 120.degree. C., and more preferably 50.degree. C.
to 100.degree. C.
At the time of curing, the photopolymer may be in state of being
injected into or coated onto a predetermined substrate or mold.
Meanwhile, as the method of recording a visual hologram on a
hologram recording medium produced from the photopolymer
composition, generally known methods can be used without particular
limitation. The method described in the holographic recording
method of the embodiment described hereinafter can be adopted as an
example.
According to another embodiment of the present disclosure, a
holographic recording method may be provided, which includes
selectively polymerizing photoreactive monomers contained in the
photopolymer composition using electromagnetic radiation.
As described above, through the process of mixing and curing the
photopolymer composition, it is possible to produce a medium in
which no visual hologram is recorded, and a visual hologram can be
recorded on the medium through a predetermined exposure
process.
A visual hologram can be recorded on the media provided through the
process of mixing and curing the photopolymer composition, using
known devices and methods under commonly known conditions.
According to another embodiment of the present disclosure, an
optical element including the hologram recording medium may be
provided.
Specific examples of the optical element include optical lenses,
mirrors, deflecting mirrors, filters, diffusing screens,
diffraction elements, light guides, waveguides, holographic optical
elements having projection screen and/or mask functions, media of
optical memory systems and light diffusion plates, optical
wavelength multiplexers, reflection-type or transmission-type color
filters, and the like.
An example of the optical element including the hologram recording
medium may include a hologram display device.
The hologram display device includes a light source unit, an input
unit, an optical system, and a display unit. The light source unit
is a part that irradiates a laser beam used for providing,
recording, and reproducing three-dimensional image information of
an object in the input unit and the display unit. Further, the
input unit is a part that previously inputs three-dimensional image
information of an object to be recorded on the display unit, and
for example, three-dimensional information of an object such as the
intensity and phase of light for each space can be input into an
electrically addressed liquid crystal SLM, wherein an input beam
(212) may be used. The optical system may include a mirror, a
polarizer, a beam splitter, a beam shutter, a lens, and the like.
The optical system can be distributed into an input beam for
sending a laser beam emitted from the light source unit to the
input unit, a recording beam for sending the laser beam to the
display unit, a reference beam, an erasing beam, a reading beam,
and the like.
The display unit can receive three-dimensional image information of
an object from an input unit, record it on a hologram plate
composed of an optically addressed SLM, and reproduce the
three-dimensional image of the object. Herein, the
three-dimensional image information of the object can be recorded
via interference of the input beam and the reference beam. The
three-dimensional image information of the object recorded on the
hologram plate can be reproduced into a three-dimensional image by
the diffraction pattern generated by the reading beam. The erasing
beam can be used to quickly remove the formed diffraction pattern.
Meanwhile, the hologram plate can be moved between a position at
which a three-dimensional image is input and a position at which a
three-dimensional image is reproduced.
Advantageous Effects
According to the present disclosure, a photopolymer composition
which can more easily provide a photopolymer layer having a high
refractive index modulation value even with a thin thickness, a
hologram recording medium including a photopolymer layer having a
high refractive index modulation value even with a thin thickness,
an optical element including the hologram recording medium, and a
holographic recording method including selectively polymerizing
photoreactive monomers contained in the photopolymer composition
using electromagnetic radiation are provided.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Hereinafter, the present invention will be explained in detail with
reference to the following examples. However, these examples are
only to illustrate the invention, and the scope of the invention is
not limited thereto.
Preparation Example: Synthesis of Polyol
34.5 g of methyl acrylate, 57.5 g of butyl acrylate, and 8 g of
4-hydroxybutyl acrylate were placed in a 2 L jacket reactor and
diluted with 150 g of ethyl acetate. Stirring was continued for
about 1 hour while maintaining the temperature of the jacket
reactor at 60 to 70.degree. C. Then, 0.035 g of n-dodecyl mercaptan
was further added to the reactor, followed by further stirring for
about 30 minutes. Thereafter, 0.04 g of AIBN
(2,2'-azo-bisisobutyronitrile) as a polymerization initiator was
added thereto, and polymerization was continued for about 4 hours
at a temperature of about 70.degree. C. until the residual
acrylate-based monomer content became 1 wt % to synthesize a
polyol. The obtained polyol had a weight average molecular weight
using polystyrene calibration measured by GPC of about 700,000 and
OH equivalent weight measured by a KOH titration method of 1802
g/OH mol.
Examples and Comparative Examples: Preparation of Photopolymer
Composition
39.44 g of the polyol of the preparation example, 31.33 g of the
monomer shown in Tables 1 to 2, 0.06 g of safranin O (dye,
manufactured by Sigma-Aldrich), 2.01 g of N-methyl diethanolamine
(manufactured by Sigma-Aldrich), 4.19 g of
[4-methylphenyl-(4-(2-methylpropyl)phenyl)]iodonium
hexafluorophosphate (Irgacure 250), and 0.42 g of BYK-310
(dispersant) were mixed with light blocked, and stirred with a
paste mixer for about 2 minutes to obtain a transparent coating
solution.
7.56 g of MFA-75X (hexafunctional isocyanate, diluted to 75 wt % in
xylene, manufactured by Asahi Kasei) was added to the coating
solution and further stirred for about 1 minute. DBTDL (0.05 wt %
with respect to the synthesized urethane resin) as a catalyst was
added thereto and stirred for about 1 minute. It was coated on a PC
substrate (125 .mu.m) using a Mayer bar to a thickness of 18 .mu.m,
and then cured at 80.degree. C. for 30 minutes. Thereafter, the
sample was allowed to stand for 12 hours or more in a dark room
under constant temperature and humidity conditions of about
25.degree. C. and 50 RH %.
Experimental Examples: Holographic Recording
(1) The photopolymer-coated surfaces prepared in each of the
examples and comparative examples were laminated on a slide glass,
and fixed so that a laser first passed through the glass surface at
the time of recording.
(2) A holographic recording was done via interference of two
interference lights (reference light and object light), and a
transmission-type recording was done so that the two beams were
incident on the same side of the sample. The diffraction
efficiencies change with the incident angle of the two beams, and
become non-slanted when the incident angles of the two beams are
the same. In the non-slanted recording, the diffraction grating is
generated perpendicularly to the film because the incident angles
of the two beams are equal to a normal line.
The recording (2.theta.=45.degree.) was done in a transmission-type
non-slanted manner using a laser with a wavelength of 532 nm, and
the diffraction efficiency (.eta.) was calculated according to the
following Equation 1.
.eta..times..times. ##EQU00001##
In Equation 1, .eta. is a diffraction efficiency, P.sub.D is an
output amount (mW/cm.sup.2) of the diffracted beam of a sample
after recording, and P.sub.T is an output amount (mW/cm.sup.2) of
the transmitted beam of the recorded sample.
The lossless dielectric grating of the transmission-type hologram
can calculate the refractive index modulation value (.DELTA.n) from
the following Equation 2.
.eta..function..function..function..pi..DELTA..times..times..lamda..theta-
..times..times. ##EQU00002##
In Equation 2, d is a thickness of the photopolymer layer, .DELTA.n
is a refractive index modulation value, .eta.(DE) is diffraction
efficiency, and .lamda. is a recording wavelength.
TABLE-US-00001 TABLE 1 Types of mono/polyfunctional acrylate
monomer of examples and measurement results of refractive index
modulation values (.DELTA.n) Examples 1 to 3 Example 1 Example 2
Example 3 Types of mono/polyfunctional acrylate monomer
Monofunctional Polyfunctional Polyfunctional Polyfunctional
acrylate monomer acrylate monomer acrylate monomer acrylate monomer
[M1142 (Miwon)] [M282 (Miwon)] [M284 (Miwon)] [M3130 (Miwon)]
Refractive index 1.59 1.475 1.476 1.492 Tg (.degree. C.) 33 14 -13
40 Mw 268 308 408 428 Viscosity (cps, 25.degree. C.) 150 25 40 60
Weight ratio relative 0.2 0.2 0.2 to all monomers .DELTA.n 0.0123
0.0123 0.0122
TABLE-US-00002 TABLE 2 Types of mono/polyfunctional acrylate
monomer of Comparative Examples and measurement results of
refractive index modulation value (.DELTA.n) Comp. Exs. 1 Comp.
Comp. Comp. Comp. Comp. Comp. Comp. to 7 Ex. 1 Ex. 2 Ex. 3 Ex. 4
Ex. 5 Ex. 6 Ex. 7 Types of mono/polyfunctional acrylate monomer
Mono- Poly- Poly- Poly- Poly- Poly- Poly- Poly- functional
functional functional functional functional functional functio- nal
functional acrylate acrylate acrylate acrylate acrylate acrylate
acrylate acrylate monomer monomer monomer monomer monomer monomer
monomer monomer [M1142 [M282 [M284 [M3130 [M2100 [M2100 [M244 [M244
(Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)]
(Miwon)] Refractive 1.59 1.475 1.476 1.492 1.529 1.529 1.557 1.557
index Tg (.degree. C.) 33 14 -13 40 -7 -7 67 67 Mw 268 308 408 428
776 776 468 468 Viscosity 150 25 40 60 660 660 1730 1730 (cps,
25.degree. C.) Weight 0.4 0.4 0.4 0.4 0.2 0.4 0.2 ratio relative to
all monomers .DELTA.n 0.0118 0.0118 0.0114 0.0115 0.0117 0.0108
0.0109
1) Measurement of Refractive Index of Monomers
Irgacure 184 (UV initiator, manufactured by Ciba) and F477
(surfactant, manufactured by DIC) were used in an amount of 0.5 wt
% and 0.2 wt % relative to the monomer, respectively, to prepare a
coating solution. The coating solution was coated on a glass
substrate to a thickness of 2 .mu.m and dried at 60.degree. C. for
2 minutes. After curing by irradiating ultraviolet rays at 150
mJ/cm.sup.2, the refractive index was measured at 632.8 nm using
SPA-3DR.
2) Measurement of Glass Transition Temperature (Tg) of Monomers
Irgacure 184 (UV initiator, manufactured by Ciba) was used in an
amount of 0.5 wt % relative to the monomer to prepare a coating
solution. The coating solution was coated on a glass substrate to a
thickness of 10 .mu.m and dried at 60.degree. C. for 2 minutes.
After curing by irradiating ultraviolet rays at 150 mJ/cm.sup.2,
the film was peeled off and the glass transition temperature of the
film was measured using DSC. Specifically, when using DSC, the
temperature was increased from -100.degree. C. to 200.degree. C. at
a rate of 10.degree. C./min and decreased from 200.degree. C. to
-100.degree. C. at a rate of -10.degree. C./minute. This process
was repeated twice, and the glass transition temperature was
confirmed at the second heating period.
As shown in Tables 1 and 2 above, it was confirmed that the
examples using a photoreactive monomer including a polyfunctional
(meth)acrylate monomer having a refractive index of 1.5 or less and
a viscosity at 25.degree. C. of 100 cps or less, and a
monofunctional (meth)acrylate monomer having a refractive index of
1.5 or more, wherein a content of the monofunctional (meth)acrylate
monomer is 60 wt % or more, can provide holograms exhibiting a
significantly improved refractive index modulation value as
compared with the comparative examples even with a thin
thickness.
* * * * *